1. Field of the Inventive Concepts
The inventive concepts disclosed and claimed herein relate to methods for making pigment for plastics applications, more particularly, but not by way of limitation, to methods of surface treating pigment for plastics applications such that micronization is not necessary.
2. Brief Description of Related Art
Particulate inorganic pigments are used as opacifiers and colorants in many industries, including the coatings, plastics, and paper industries. Titanium dioxide is the most widely used white pigment in commerce today due to its ability to confer high opacity when formulated into end-use products. Titanium dioxide pigments, are generally micronized to form a finely divided powder and thereby maximize the opacifying properties imparted to materials formulated therewith.
The effectiveness of the particulate pigment in such plastics applications depends, in part, on how evenly the pigment can be dispersed in the polymer melt. Titanium dioxide particles typically have a hydrophilic surface, making them difficult to incorporate in hydrophobic materials such as plastics. Without proper surface treatment, even mixing for long periods of time with high energy levels does not achieve good dispersion. In addition, titanium dioxide powders are inherently dusty and frequently exhibit poor powder flow characteristics during the handling of the powder itself, especially during formulation, compounding, and manufacture of end-use products.
To this end, physical and chemical modification of titanium dioxide particle surfaces has been used to improve the properties of titanium dioxide particles in polymer matrices. Such improvements sought include improved flow characteristics, decreased chemical activity, and improved thermal stability, especially lacing resistance in extruded polymer film applications. Surface treatment agents are added to the particulate titanium dioxide to provide a hydrophobic surface for use in plastics. The titanium dioxide pigment particles are micronized to achieve sufficient de-agglomeration of the pigment particles prior to compounding the pigment with a polymer to produce a polymer concentrate. High performance titanium dioxide master batches have been formulated with increased concentrations of titanium dioxide in the polymer concentrated, making downstream polymer product processing easier and delivering excellent product uniformity and lacing resistance.
To date, high performance master batch research has focused on surface treatment with hydrophobic compounds and has always included micronization. Despite the significant research done in this area, there remains a need for improvements in the economical surface treatment of particulate titanium dioxide that provides improved handling, dispersion and final product properties without the need for micronization.